Cancers have long represented a challenge to modem medicine. Classical cancer therapy can generally provide the following measures:
1. Surgical removal of the tumor
2. Chemotherapy
3. Radiotherapy
4. A combination of the three above measures.
Despite all the advances in the measures listed above, tumors or metastases can recur in many patients. Depending on the state of health of the patient, their age and the type of tumor, the forms of therapy described above can be repeated. However it can also occur that a patient is “therapied out”, meaning that the above-mentioned classical therapy measures can no longer be employed, since the patient can no longer endure the stress of these therapies physically and/or mentally.
For such “therapied out” patients the practice of applying strong painkillers is known, some of which can also be introduced directly via a catheter into the tumor area. In such cases however this only fights the pain, no healing is achieved.
Thus in recent times so-called tumor ablation has been recommended as a new method of treatment. This makes provision for guiding a tool, for example a catheter or a biopsy needle, to the tumor or the metastasis and damaging the tumor with the aid of various forms of energy or by injection of alcohol.
What is referred to as thermoablation will be described here in greater detail by way of example. Radio frequency (RF), microwave, ultrasound and/or laser energy is used for thermoablation. In such cases the tumor cells are killed by high temperatures, while healthy tissue remains protected. In radio frequency ablation (RFA) an interventional radiologist, with the aid of imaging technologies, introduces a thin needle into the patient's tumor. Radiofrequency energy is transferred from the tip of the needle to the target tissue, where it generates great heat and thereby kills the tumor. The dead tissue shrinks and slowly forms a scar.
Depending on the size of the tumor, RFA can cause it to shrink or can kill it, whereby the life of a patient can be extended and their quality of life significantly improved. Since RFA involves a local method which has little or no adverse effect on healthy tissue, the treatment can be repeated frequently.
Pain caused by tumors and also other symptoms of weakness are mitigated by the size of the tumor being reduced or by new tumors which occur being treated. Although the tumors themselves often cause no pain, they can press on nerves or vital organs, which causes great pain under some circumstances. RFA can be employed for small to medium-size tumors, cf. the article by Zhengium Liu entitled “Radiofrequency tumor ablation”, AJR: 184, April 2005, 1347 to 1352.
A great disadvantage of the above ablation therapy is that this can only be used with relatively small tumors. A very high proportion of tumors is discovered at a relatively late stage however and can thus no longer be treated by this form of therapy.
An alternative to ablation is so-called radio embolization, also called selective internal radiotherapy (SIRT). In such cases the vessels are sealed off with radioactive microcapsules, frequently having a spherical shape. These tiny spheres have an approximate diameter of five red blood corpuscles and attach themselves to the blood vessels of the tumor, from where they emit radiation which damages and especially kills the tumor cells.
The radioisotope Yttrium-90 is frequently used, with the microcapsules containing the radioisotope being produced immediately before the intervention and brought to the treatment clinic. Yttrium-90 is used by preference since it involves a pure Beta radiator. Thus the undesired radiation exposure for persons in the immediate environment is low and 90% of the energy of the particle radiation is deposited in the tissue within a radius of approx. 9 to 11 mm. The comparatively short physical half-life only requires a short stay in the nuclear medical clinic, for example of around 48 hours.
The production of such radioactive therapeutic agents or of corresponding microcapsules is described in US 2004/0076582 for example.
Radioembolization is carried out as a visually-controlled therapy by an interventional radiologist in collaboration with a nuclear medical expert. After a local anesthetic a thin catheter is introduced into the artery via a small skin puncture in the strip. This catheter is then moved under flouroscopy control to the target location, i.e. the tumor. For the treatment of a liver tumor the catheter can be guided under fluoroscopy control along the liver artery (Arteria Hepatica). The radioactive isotope is injected through the catheter in the form of microcapsules, especially microspheres, directly into those artery branches which supply the tumor, especially the liver tumor. These microspheres remain lodged in the tumor vessels where they emit their tumor-killing radiation. This radiation is restricted to this area, its dose can be correspondingly higher without any collateral damage being caused to healthy tissue during the treatment.
Radio embolization generally involves a palliative treatment method, which means that it does not heal the cancer. Despite this patients profit greatly from this method since their life expectancy is increased by it and their quality of life is improved. The therapy approach involved is a relatively new one but it has already shown successes in the treatment of primary tumors or metastases. To date fewer side-effects have been identified with this treatment method than for example with typical chemotherapies.
Radio embolization is used for example in hepatocellular carcinomas (HCC), for cholangiocellular carcinomas and with liver metastases such as of intestinal and breast cancer or of other malignomas. The most frequent side-effects which occur are tiredness, which can last for seven to ten days.
A disadvantage of this method is that, if the radioactive microcapsules find their way into the lungs, gall bladder or stomach, they can cause radiation damage there.
A further new very promising treatment method is so-called “magnetic drug targeting” in which chemotherapeutic-laden magnetic nanoparticles are introduced into the tumor via a catheter or a puncturing needle. Subsequently the magnetic nanoparticles are concentrated by a magnet in the area of the greatest field gradient and then release the chemotherapeutic medicament in the tumor. Magnetic nanoparticles for therapy purposes are known for example from U.S. Pat. No. 6,514,481 B1.
The microcapsules or microspheres currently used mostly consist of a magnetic core, namely the magnetic nanoparticle, onto which the chemotherapeutics which lead to the destruction of the tumor cells are coated as an envelope.
As already indicated, these nanoparticles can be guided by magnetic fields in the room to a specific target location or held there, i.e. in the tumor volume for example, in order to act locally and selectively. In order to exert such magnetic holding forces inhomogeneous magnetic fields, especially with strong gradients (gradient field) are required which can be generated for example by an electromagnet but also by permanent magnets.
The magnetic gradient field is designed in such cases so that a spatial region, the so-called focus, exists within which the generated holding forces are at their maximum. In such cases it is frequently difficult to get this focus to cover the target location, with this operation currently frequently being performed manually on the basis of visual information or suchlike, which involves the risk of the treatments not having an effect or not having a sufficient effect at the target location. The positioning is then based on a purely optical estimation by the doctor, whereby a concentration at the incorrect point means that healthy sections of tissue can be damaged or thromboses can be created by accumulation of the microcapsules at the incorrect point.